Ruthenium-catalyzed cycloaddition of 1,6-diynes and nitriles under mild conditions: Role of the coordinating group of nitriles

In the presence of a catalytic amount of [Cp*RuCl(cod)] (Cp* = pentamethylcyclopentadienyl, cod=1,5-cyclooctadiene), 1,6-diynes were allowed to react chemo- and regioselectively with nitrites bearing a coordinating group, such as dicyanides or alpha-halonitriles, at ambient temperature to afford bicyclic pyridines. Careful screening of nitrile components revealed that a C C triple bond or heteroatom substituents, such as methoxy and methylthio groups, proved to act as the coordinating groups, whereas C=C or C=0 double bonds and amino groups failed to promote cycloaddition. This suggests that coordinating groups with multiple it-bonds or lone pairs are essential for the nitrile components.